1. Field of the Invention
The present invention relates to a method for controlling the gear-transmission of a vehicle, and more particularly to a controlling method for vehicular gear transmissions which is suitable for shifting the vehicular gear transmission to the appropriate gear position in the case where ordinary detection of vehicle running speed becomes impossible.
2. Description of the Prior Art
In the prior art there have been proposed various vehicle transmission control systems for shifting a vehicular gear transmission to the gear position suitable for the vehicle running speed at that time. In the conventional control system of such type, various back-up control systems have been proposed for securing transmission control operation even if it becomes impossible to determine the vehicle running speed by the vehicle speed sensor. For example, Japanese Patent Application Public Disclosure No. 11753/85 discloses a transmission control system having a back-up system by which the gear-shifting operation of the vehicular transmission is carried out in accordance with vehicle speed data calculated from the current gear position and the engine rotational speed, which is equal to the rotational speed on the input side of the transmission in the case where the gear-transmission is shifted to a position other than its neutral position. Furthermore, this disclosed system is arranged to store the vehicle speed data calculated just before the gear transmission is shifted to its neutral position, and the stored vehicle speed data is used for controlling the gear-shifting operation of the gear-transmission when the gear transmission is shifted out of its neutral position.
However, according to the disclosed control system, when the gear transmission is shifted into the neutral gear position when the vehicle is running down hill, the actual vehicle speed becomes higher than the vehicle speed data stored just after the gear transmission was shifted into the neutral position. As a result, the gear-transmission may be shifted into a position different from the position suitable for the actual vehicle speed just before the selecting lever is moved from the neutral position to the drive position, whereby the gear transmission is sometimes damaged. A similar disadvantage arises in the case where the driver moves the selecting lever from the neutral position to the reverse position at the time when the actual vehicle speed has become greater than zero because of down-hill running of the vehicle, even though the calculated vehicle speed obtained just before the gear-transmission was shifted to the neutral position is zero.